$inc¶

Definition定义¶

$inc¶

The $inc operator increments a field by a specified value and has the following form:$inc运算符按指定值递增字段，其形式如下：

{ $inc: { <field1>: <amount1>, <field2>: <amount2>, ... } }

To specify a <field> in an embedded document or in an array, use dot notation.若要在嵌入式文档或数组中指定一个<field>，请使用点表示法。

Behavior行为¶

The $inc operator accepts positive and negative values.$inc运算符接受正值和负值。

If the field does not exist, $inc creates the field and sets the field to the specified value.如果该字段不存在，$inc将创建该字段并将该字段设置为指定值。

Use of the $inc operator on a field with a null value will generate an error.在具有null值的字段上使用$inc运算符将生成错误。

$inc is an atomic operation within a single document.$inc是单个文档中的原子操作。

Example示例¶

Consider a collection products with the following document:考虑一个集合products带有以下文档：

{
  _id: 1,
  sku: "abc123",
  quantity: 10,
  metrics: {
    orders: 2,
    ratings: 3.5
  }
}

The following update() operation uses the $inc operator to decrease the quantity field by 2 (i.e. increase by -2) and increase the "metrics.orders" field by 1:下面的update()操作使用$inc运算符将quantity字段减少2（即增加-2），并将"metrics.orders"字段增加1：

db.products.update(
   { sku: "abc123" },
   { $inc: { quantity: -2, "metrics.orders": 1 } }
)

The updated document would resemble:更新后的文件类似于：

{
   "_id" : 1,
   "sku" : "abc123",
   "quantity" : 8,
   "metrics" : {
      "orders" : 3,
      "ratings" : 3.5
   }
}